1. Field of the Invention
The present invention relates to a fuel cell stack formed by stacking an electrolyte electrode assembly and a pair of separators in a stacking direction, the electrolyte electrode assembly being interposed between the pair of separators. The electrolyte electrode assembly includes a pair of electrodes and an electrolyte interposed between the electrodes. Rectangular end plates are provided at both ends of the fuel cell stack in the stacking direction.
2. Description of the Related Art:
For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (MEA) which includes an anode, a cathode, and an electrolyte membrane interposed between the anode and the cathode. The electrolyte membrane is a solid polymer ion exchange membrane. The membrane electrode assembly and separators sandwiching the membrane electrode assembly make up a unit cell. In use, generally, a predetermined number of unit cells are stacked together to form a fuel cell stack mounted in a vehicle.
Mostly, the fuel cell stack of this type adopt internal manifold structure where a fuel gas supply passage and a fuel gas discharge passage as passages of a fuel gas, an oxygen-containing gas supply passage and an oxygen-containing gas discharge passage as passages of an oxygen-containing gas, and a coolant supply passage and a coolant discharge passage as passages of a coolant extend through the unit cells in the stacking direction.
As a technique related to the internal manifold type fuel cell, for example, Japanese Laid-Open Patent Publication No. 2000-260439 is known. In Japanese Laid-Open Patent Publication No. 2000-260439, as shown in FIG. 12, a spacer 1 forming a coolant channel is provided. In a marginal area 2 of the spacer 1, holes 3 and holes 4 are formed at upper and lower positions as channels of one and other of reactant gases. A pair of holes 5a and a pair of 5b are provided on both sides of the marginal area 2 as coolant channels. The pair of holes 5a, 5b are connected to a coolant space 7 through connection channels 6.
In the fuel cell, the pair of holes 5a as the coolant supply channels may be connected together and the pair of holes 5b as the coolant discharge channels may be connected together by a single supply manifold and a single discharge manifold provided in the end plates.
For example, in the case where the supply manifold has a rectangular shape, the internal volume of the supply manifold is large. Therefore, when the coolant flows into the supply manifold through a supply pipe connected to the supply manifold, the flow rate of the coolant tends to be decreased significantly. Therefore, the pressure loss of the coolant in the supply manifold increases considerably, and a vortex flow of the coolant may be generated in the supply manifold. As a consequence, the coolant cannot be supplied suitably to the pair of holes 5a. The same problem may occur also in the discharge manifold.
Further, normally, at the center of the supply manifold, an inlet pipe for supplying the coolant into the supply manifold is provided at the center of the supply manifold. Further, an outlet pipe for discharging the coolant from the discharge manifold is provided at the center of the discharge manifold. That is, the coolant supplied into the center of the supply manifold is distributed to the pair of left and right holes 5a, and the coolant discharged from the left and right pair holes 5b are merged at the center of the discharged manifold.
However, in the structure, it is difficult to allocate the same flow rate of coolant to the pair of left and right holes 5a. Therefore, the temperature distribution in the surfaces of the fuel cell become non-uniform, and the power generation performance of the fuel cell is low.